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During the Middle Cambrian, western Utah (USA) occupied the deepest part of the House Range embayment along the western edge of North America and accumulated deep-water facies dominated by cm-scale, cyclically interbedded limestone-marl layers (‘rhythmites’) of the Marjum Formation. The studied section is ~500 m thick and spans the lower Drumian-lower Guzhangian. The rhythmites (cm-scale) are packaged into repeated 2-5 m-thick parasequences and larger scale eustatic sequences both characterized by more carbonate-dominated rhythmites alternating with more siliciclastic-dominated rhythmites. Previous studies of the Marjum rhythmites suggest millennial-scale interpretation for the cm-scale rhythmites, corresponding to wetter vs drier climate oscillations influencing the relative abundance of siliciclastic vs carbonate accumulation in the deep-water setting (Elrick and Hinnov, 1996; Elrick and Hinnov, 2007).We conducted a high-resolution study of a representative 35 m-thick interval of the Marjum Formation to build a floating astrochronology assuming the meter-scale parasequences represent orbital-scale frequencies modulated by the larger scale sequences (based on biostratigraphically controlled sediment accumulation rates). To capture orbital-scale frequencies and to avoid aliasing related to millennial-scale limestone-marl lithological changes, 350 rock samples were collected at minimum 10-cm-interval exclusively in the limestone layers of rhythmite couplets. Major elements (e.g., Ti, Al, K, Si), TOC and δ13C were measured on each sample to infer on paleoenvironmental and paleoclimatic conditions. To estimate the duration of the sampled interval, multiple spectral techniques will be applied on the paleoclimatic proxies using amplitude modulation, frequency ratio as well as the 405 kyr long eccentricity as a starting point for the calibration of the time scale. Having an astronomically calibrated time scale for this interval will provide 1) independent evidence assessing the millennial-scale paleoclimatic origin of the cm-scale rhythmites, and 2) refine the Cambrian time scale to better constraint the origin and rate of the Cambrian explosion events.Elrick, M. and Hinnov, L.A., 1996. Millennial-scale climate origins for stratification in Cambrian and Devonian deep-water rhythmites, western USA. Palaeogeography, Palaeoclimatology, Palaeoecology, 123(1-4): 353-372.Elrick, M. and Hinnov, L.A., 2007. Millennial-scale paleoclimate cycles recorded in widespread Palaeozoic deeper water rhythmites of North America. Palaeogeography, Palaeoclimatology, Palaeoecology, 243(3-4): 348-372.

The Cambrian Period recorded critical evolutionary events and geochemical changes. These changes, such as the “Cambrian Explosion” (Briggs, 2015; Peng et al., 2020) and the “Cambrian Substrate Revolution” (Mángano & Buatois, 2017; Peng et al., 2020) can persist for many millions of years or can be a short carbon isotopic excursion or anoxic event. Despite the significance of this period for the history of life on Earth, it features a remarkably poorly defined time scale owing to 1) the paucity of high-precision radioisotope age data, 2) the generalized endemism (especially during the lower Cambrian) and 3) the lack of well-preserved exposures.Recent advances in time-series methods for identifying Milankovitch cycles have accelerated the refinement of the Phanerozoic GTS and the invariant set of periods for the Earth’s orbital eccentricity for at least the last 600 Ma have allowed for the building of high-resolution floating astronomical time scales (ATS) for Mesozoic and Paleozoic sequences.A crucial issue in unraveling Milankovitch cyclicity in Paleozoic successions is the selection of suitable sedimentary sequences, which are able to record orbitally-forced climatic cycles continuously. A recent cyclostratigraphic study by Zhao et al. (2022) on the middle and upper portion of the Albjära-1 drill core confirmed the record of such cycles in a time interval that extends from the lower Guzhangian to the Lower Ordovician. In this study, we conducted a high-resolution (1 mm) XRF core scanning on the lower portion (27 m) of the Albjära-1 drill-core to assess Milankovitch cyclicity recorded by variations in detrital input proxies and built a floating ATS for the middle Wuliuan-lower Guzhangian interval. Our ATS is in stratigraphic continuity with Zhao et al.’s (2022) ATS, thus allowing us to use the U/Pb absolute age anchor below the Cambrian-Ordovician boundary (486.78 ± 0.53 Ma) and expand their ATS to the middle Wuliuan.The core recovery is close to 100%. The first 5 m are characterized by sandy limestone of the Gislöv Formation, and the overlying 22 m consist of deep-water black shales of the Alum Shale Formation, from which 151 samples were taken each 15 cm for δ13Corg analysis.The combination of both δ13Corg and XRF elemental analyses allows for precise integration of the ATS in the global Cambrian geochemical framework and provides better insight into the timing and origin of geochemical fluctuations during the studied time interval. REFERENCESBriggs, D. E. G. (2015). The Cambrian explosion. Current Biology, 25 (19), R864-R868. https://doi.org/10.1016/j.cub.2015.04.047Mángano, M. G., & Buatois, L. A. (2017). The Cambrian revolutions: Trace-fossil record, timing, links and geobiological impact. Earth-Science Reviews,173, 96-108. https://doi.org/10.1016/j.earscirev.2017.08.009Peng, S.-C., Babcock, L. E., & Ahlberg, P. (2020). The Cambrian Period. In F. Gradstein, J. G. Ogg, M. D. Schmitz, & G. M. Ogg (Eds.), Geological Time Scale 2020 (Vol. 2, pp. 565-629). Elsevier. https://doi.org/10.1016/B978-0-12-824360-2.00019-XZhao, Z., Thibault, N.R., Dahl, T.W., Schovsbo, N.H., Sørensen, A.L., Rasmussen, C.M.Ø., and Nielsen, A.T. (2022). Synchronizing rock clocks in the late Cambrian. Nature Communications, 13, 1-11. https://doi.org/10.1038/s41467-022-29651-4

The Cambrian Explosion is a fundamental turning point in the evolution of life that occurred during the Cambrian Period (~541 to ~485 million years ago), which involved the origination and explosive radiation of all major animal phyla. The bursts of evolution characterizing this period appear concurrently with major modifications to the physico-chemical conditions of the world’s oceans, and are recorded in critical fossil localities where soft-tissues are exceptionally well preserved, including Lagerstätten such as the Burgess Shale and Chengjiang Biota. As a result of the severe lack of biostratigraphically-correlatable fossils (due to widespread endemism during the Cambrian) and sparse high-precision radioisotopic dates, the Cambrian time scale remains among the least defined stage of all the Phanerozoic Eon, with a minimum uncertainty of ±2 million years at its stage boundaries. The absence of a high-resolution geological time scale for the Cambrian Explosion hampers our ability to robustly address widely debated questions concerning the origins and rates of the evolutionary and ecological events, their relationship with paleoceanographic conditions, their responses to astronomically-forced climate change, including from Milankovitch “grand” cycles, and whether these events were globally synchronous.Using an integrated set of geophysical/chemical proxies with advanced time series techniques on selected stratigraphic sections, this project aims at (1) Generate sets of high- resolution geophysical and geochemical stratigraphic proxies enabling to capture Milankovitch forcing within the selected sedimentary records, (2) Building a high-resolution time scale to improve our knowledges on the timing of major Cambrian evolutionary milestones and geochemical changes and (3) Determine the relationships between Cambrian evolutionary and ecological events with the paleoceanographic changes and Milankovitch cycles.

ICP-OES dataset, Matlad and R scripts.

The Late Devonian biosphere was affected by two of the most severe biodiversity crises in Earth's history, the Kellwasser and Hangenberg events near the Frasnian–Famennian (F–F) and the Devonian–Carboniferous (D–C) boundaries, respectively. Current hypotheses for the causes of the Late Devonian extinctions are focused on climate changes and associated ocean anoxia. Testing these hypotheses has been impeded by a lack of sufficient temporal resolution in paleobiological, tectonic and climate proxy records. While there have been recent advances in astronomical calibration that have improved the accuracy of the Frasnian time scale and part of the Famennian, the time duration of the entire Famennian Stage remains poorly constrained. During the Late Devonian, a complete Late Frasnian–Early Carboniferous succession of deep-shelf deposits accumulated in the epieric sea in Illinois Basin of the central North-American mid-continent. A record of this sequence is captured in three overlapping cores (H-30, Sullivan and H-32). The H-30 core section spans the F–F boundary; the Sullivan section spans almost all of the Famennian and the H-32 section sampled spans the interval of the Upper Famennian and the D–C boundary. To have the best chance of capturing Milankovitch cycles, 2000 rock samples were collected at minimum 5-cm-interval across the entire sequence. Magnetic susceptibility (MS) was measured on each sample and the preservation of climatic information into the MS signal was verified through geochemical analyses and low-temperature magnetic susceptibility acquisition. To estimate the duration of the Famennian Stage, we applied multiple spectral techniques and tuned the MS signal using the highly stable 405 kyr cycle for Sullivan and the obliquity cycle for the H-30 and H-32 cores. Based on the correlation between the cores we constructed a Famennian floating astronomical time scale, which indicates a duration of 13.5 ± 0.5 myr. An uncertainty of 0.5 myr was estimated for the uncertainties arising from the errors in the stratigraphic position of the F–F and D–C boundaries, and the 405 kyr cycle counting. Interpolated from the high-resolution U–Pb radiometric ages available for the Devonian–Carboniferous boundary we recalibrated the Frasnian–Famennian boundary numerical age to 372.4 ± 0.9 Ma.

In this paper we formulate answers to three important questions related to Givetian carbonate records and their use for reconstructing million-year-scale past palaeoenvironmental changes. First, we provide detailed illustrations of the fascinating diversity that shaped a significant shallow reefal platform during early to late Givetian time in the Rhenohercynian Ocean; secondly we improve the sedimentological model of the extensive Givetian carbonate platform in the Dinant Basin; and thirdly we evaluate the application of magnetic susceptibility as a tool for long-term trend correlations and palaeoenvironmental reconstructions. These goals are reached by making a sedimentological, geophysical and geochemical study of the La Thure section. Through the early–late Givetian interval we discerned 18 microfacies ranging from a homoclinal ramp to a discontinuously rimmed shelf and then a drowning shelf. The comparison of these sedimentological results with those published for the south of the Dinant Syncline allowed us to provide an up to date model of the vertical and lateral environmental development of one of the largest Givetian carbonate platforms in Europe. This comparison also increased the knowledge on the distribution of facies belts in the Dinant Basin and allowed us to highlight the Taghanic Event. Palaeoredox proxies reveal a substantial change in the oxygenation level, from oxygen-depleted to more oxic conditions, between middle and late Givetian time. We demonstrated the relationship between variation in magnetic susceptibility values and proxies for siliciclastic input (such as Si, Al). The La Thure section is considered a key section for the understanding of internal shelf settings bordering Laurussia9s southeastern margin.

A rich assemblage of Middle Devonian (late Eifelian) polychaete jaws (scolecodonts) from the Blankenheimerdorf section in the type Eifel area, western Germany, is described. The top part of the section also reflects the onset of the global Kacak Event. The sediments of the section were deposited in a shallow to deep subtidal environment on the southern Avalonian margin. The habitat was obviously favourable for jaw-bearing polychaetes, which are represented by 18 species belonging to 9 genera. The assemblage is dominated by polychaetaspids, followed by mochtyellids, paulinitids and kielanoprionids. Notably, this study documents one of the oldest records of kielanoprionids, a polychaete family common since the Middle Devonian and closely related to the extant Hartmaniellidae. This may indicate that a prominent change in jawed polychaete evolution occurred during the Early–Middle Devonian transition. Moreover, we present new information on polychaete palaeobiogeography, which when compared with previously described Devonian scolecodonts shows that very similar polychaete faunas with many species in common were widespread in today's Europe and North America.

Recent opening of the La Thure quarry in Western Belgium allowed the collection of new data from a poorly outcropping area of the Belgian Frasnian platform. The studied section covers an interval extending from the falsiovalis to hassi s.l. Zones. Sedimentological analyses allowed the reconstruction of depositional settings in the northwestern part of the Dinant Synclinorium after the demise of the extended Givetian carbonate platform. Two depositional models are distinguished: (a) siliciclastic drowned platform during the Early Frasnian; and (b) a fore-reef depositional setting belonging to a rimmed shelf during the Middle Frasnian. Moreover, interpreted depositional settings in the northwestern part of the Dinant Synclinorium allowed to constraint the direction of the main facies belts for the Belgian Frasnian platform. Combination of MS and geochemistry demonstrates the inherent-parallel link existing between variation in MS values and proxy for terrestrial input (such as Si and Al). This observation meansthat, despite the remagnetization occurring within the Belgian Frasnian lithologies, the main trends in the MS signal from the La Thure section still reflect some syn-sedimentary conditions. The increase in MS and clastic input proxies recorded in distal fore-reef deposit within the punctata Zone are likely to be considered as enhanced by rapid and strong shallowing events recognized in the 'puncata Event' interval.

The Brilon-reef complex is one of the biggest Devonian carbonate buildups (*80 km 2 ) of the Rhei- nisches Schiefergebirge. The Burgberg section is located in the southeastern fore-reef area of the Brilon Reef Complex and exposes a succession of strata (117 m thick), which extends from the Middle Givetian (middle varcus conodont Zone) to the Visean (bilineatus cono- dont Zone). Field and microfacies observations led to the definition of nine microfacies that are integrated into a sedimentary model divided into off-reef, intermediate fore-reef, and proximal fore-reef sedimentary domains (SD). The off-reef domain (SD1) is the most distal set- ting observed and is characterized by fine-grained sedi- ments, dominated by pelagic biota and the local occurrence of gravity-flow deposits. The intermediate fore-reef (SD2) is characterized by a mixture of biota and sediments coming from both deeper-water and shallow-water sources and is influenced by storm and gravity-flow currents. In this domain, Renalcis mound- like structures developed locally. Finally, the proximal fore-reef (SD3) corresponds to the most proximal setting that is strongly influenced by gravity-flow currents derived from the Brilon Reef Complex. The temporal evolution of microfacies in the fore-reef setting of the Burgberg section show five main paleoenvironmental trends influenced by the onset, general development, and demise/drowning of the Brilon Reef Complex. Fore-reef to off-reef lithologies and their temporal changes are from the base to the top of the section: (U1)—fine- grained sediments with large reef debris, corresponding to the initial development of the reef building upon submarine volcaniclastic deposits during the Middle Givetian (middle varcus Zone) and first export of reef debris in the fore-reef setting; (U2)—high increase of reef-derived material in the fore-reef area, corresponding to a significant progradation of the reef from the Middle Givetian to the Early Frasnian (maximum extension of the Brilon Reef Complex to the south, disparilis to the falsiovalis conodont biozones); (U3)—progressive decrease of shallow-water derived material and increase of fine-grained sediments and deep-water biota into the fore-reef setting, corresponding to the stepwise with- drawal of the reef influence; from the Middle to the Late Frasnian (jamieae conodont Zone); (U4)—development of a submarine rise characterized by nodular and ceph- alopod-bearing limestones extending from the Late Frasnian to the Late Famennian corresponding to the demise and drowning of the Brilon Reef Complex as a result of the Late Frasnian Kellwasser events (upper rhenana and triangularis conodont biozones); (U5)— significant deepening of the Burgberg area starting in the Late Famennian, directly followed by an aggrading trend marked by pelagic shales overlying the nodular limestone deposits.

This sedimentological study of the Godavari quarry is the first relating to the Palaeozoic Tethyan sedimentary rocks of the Kathmandu nappe (Central Nepal). Sedimentological analyses led to the identification of six microfacies belonging to a large carbonate mud-mound complex, which can be divided into mound, flank and off-mound main depositional settings. Identification of two dasycladaceans (Dasyporella cf. silurica ( Stolley, 1893 ) and Vermiporella sp.) in the mound facies gives a Mid-Late Ordovician age to this newly discovered Godavari carbonate mud-mound, which makes this mound one of the oldest ever described in the Asian continent. The mound microfacies are characterized by a high micritic content, the presence of stromatactis and the prevalence of red coloured sediments (the red pigmentation probably being related to organic precipitation of iron). The flank microfacies are characterized by a higher crinoid and argillaceous content and the presence of bio- and lithoclasts concentrated in argillaceous lenses. Finally, the off-mound microfacies show very few bioclasts and a high argillaceous content. Palaeoenvionmental interpretation of microfacies, in terms of bathymetry, leads us to infer that the Godavari mud-mound started to grow in a deep environment setting below the photic and wave action zones and that it evolved to occupy a location below the fair weather wave base. Cementation of cavities within the mound facies underlines a typical transition from a marine to a burial diagenetic environment characterized by: (1) a radiaxial non luminescent feroan calcite cement (marine) showing a bright orange luminescent band in its middle part; (2) a bright zoned orange fringe of automorphic feroan calcite (meteoric phreatic); (3) a dull orange xenomorphic feroan calcite cement in the centre of cavities (burial) and (4) a saddle dolomite within the centre of larger cavities. The faunal assemblage (diversity and relative proportion) of the Godavari mound facies is dominated by crinoids and ostracods, which makes this carbonate mud-mound comparable to the Meiklejohn Peak mounds (Nevada).

This study focuses on the base of the Eifelian stage and on the abandoned Ohlesberg quarry. The exposed section (92 m thick) is related to the Lauch and Nohn formations. Petrographic study leads to the definition of 11 microfacies which are integrated in a palaeogeographical model. It corresponds to a complex ramp setting where carbonate, mixed and siliciclastic deposits coexist. The microfacies evolution is interpreted in terms of bathymetric and lateral variations, showing a general shallowing-upward trend and transitions between carbonate-dominated and siliciclastic-dominated sedimentary domains. This interpretation is supported by trends in magnetic susceptibility data. Even if the proximity to emerged areas appears to be the major influence on magnetic susceptibility values, the influence of carbonate productivity and wave agitation is also noted. The Ohlesberg section clearly points to the local and regional complex facies architecture, and advocates to variegated depositional environments along the Mid-Eifelian High.

Recent advances in radiometric dating result in significant improvements in the geo- logical timescale and provide better insight into the timing of various processes and evolutions within the Earth's system. However, no radiometric ages are contained within the Givetian. Con- sequently, the absolute ages of the Givetian Stage boundaries, as well as the stage's duration, remain poorly constrained. As an alternative, the analysis of sedimentary cycles allows for the esti- mation of the duration of this stage. We examined the high-resolution magnetic susceptibility signals of four Givetian outcrops in the Givet area for a possible astronomical imprint, to fully understand the rates of evolutionary and environmental change. All four sections are firmly corre- lated and wavelet analyses of the magnetic susceptibility signals reveal the imprint of astronomical eccentricity forcing. The highly stable 405 kyr cycles constrain the duration of the Givetian Stage at 4.35+ 0.45 Myr, which is in good agreement with the International Chronostratigraphic Chart (5.0 Myr). The studied sections also exhibit an imprint of obliquity, suggesting a climatic telecon- nection between low and high latitudes. The corresponding microfacies curves demonstrate similar astronomical imprint, and thereby indicate that the observed 10 5 year-scale cyclicity is the result of climatic and environmental change.

The development and behavior of million year- scaled depositional sequences recorded within Palaeozoic carbonate platform has remained poorly examined. There- fore, the understanding of palaeoenvironmental changes that occur in geological past is still limited. We herein undertake a multi-disciplinary approach (sedimentology, conodont biostratigraphy, magnetic susceptibility (MS), and geochemistry) of a long-term succession in the Carnic Alps, which offers new insights into the peculiar evolution of one of the best example of Palaeozoic carbonate platform in Europe. The Freikofel section, located in the central part of the Carnic Alps, represents an outstanding succession in a fore-reef setting, extending from the Latest Givetian (in- det.falsiovalis conodont zones) to the Early Famennian (Lower crepida conodont zone). Sedimentological analysis allowed to propose a sedimentary model dominated by distal slope and fore-reef-slope deposits. The most distal setting is characterized by an autochthonous pelagic sedi- mentation showing local occurrence of thin-bedded turbi- ditic deposits. In the fore-reef slope, in a more proximal setting, there is an accumulation of various autochthonous and allochthonous fine- to coarse-grained sediments origi- nated from the interplay of gravity-flow currents derived from the shallow-water and deepwater area. The temporal evolution of microfacies in the Freikofel section evolves in two main steps corresponding to the Freikofel (Unit 1) and the Pal (Unit 2) limestones. Distal slope to fore-reef lithologies and associate changes are from base to top of the section: (U1) thick bedded litho- and bioclastic breccia beds with local fining upward sequence and fine-grained mud- stone intercalations corresponding, in the fore-reef setting, to the dismantlement of the Eifelian-Frasnian carbonate platform during the Early to Late Frasnian time (falsiovalis to rhenana superzones) with one of the causes being the Late Givetian major rift pulse; (U2) occurrence of thin- bedded red nodular and cephalopod-bearing limestones with local lithoclastic grainstone intercalations corre- sponding to a significant deepening of the area and the progressive withdrawal of sedimentary influxes toward the basin, in relation with Late Frasnian sea-level rise. MS and geochemical analyses were also performed along the Fre- ikofel section and demonstrate the inherent parallel link existing between variation in MS values and proxy for terrestrial input. Interpretation of MS in terms of palaeo- environmental processes reflects that even though distality remains the major parameter influencing MS values, car- bonate production and water agitation also play an impor- tant role.

Low-field magnetic susceptibility (?in) measurements are quick and sensitive enabling the creation of high-resolution records; making ?in an attractive correlation tool and a proxy for paleoclimate and paleoenvironments. In geologically young material – foremost in Cenozoic sediments – ?in belongs to the geoscientist's toolkit. However, ?in is a convolved signal and may reflect other processes than the often implicitly inferred depositional conditions. Diagenesis, remagnetization and low-grade metamorphism, can potentially obscure the original, depositional, ?in signal. This aspect is particularly important when interpreting ?in records from Paleozoic rocks. Here, we review data obtained from a large sample collection of Middle to Upper Devonian sections in Belgium. Comparison of ?in trends with paleoenvironmental indicators (facies) and with detrital input proxies (Zr, Th, Ti, Al) allowed to assess the persistence of depositional trends. Furthermore, the ?in signal was deconvolved into its dominant mineralogical contributions with the help of magnetic-property analysis. The main results are pointing to a magnetic signal dominated by fine-grained magnetite, of which paleomagnetic analysis indicated a formation during Carboniferous remagnetization. This prompts a potentially strong influence of post-depositional processes and it complicates the interpretation of ?in records in terms of depositional environments. However, in most of the sections, there is a relatively good relationship between ?in trends and facies evolution and between ?in and geochemical proxies for detrital inputs. This indicates that the newly formed magnetite grains would at least partly remain where they are formed, and this allows a relative preservation of the original signal, despite the strong influence of diagenesis. Two sections show a stronger impact of diagenesis, where for about half of these sections, the primary, depositional information is lost. The Eifelian–Givetian Monts de Baileux section was selected for time-series analysis of the ?in series. The Average Spectral Misfit (ASM) method is applied to explicitly evaluate the null hypothesis of no orbital signal and in this section, there is 99.05% chance that the MS signal is reflecting an orbital imprint.